1. Field of the Invention
The present invention generally relates to an electroluminescent panel and, more particularly, to a multi-color electroluminescent panel having a multi-color display capability.
2. Description of the Prior Art
An electroluminescent panel having a multi-color display capability is well known in the art. Two types of prior art multi-color electroluminescent panels are shown in FIGS. 11 and 12, respectively, of the accompanying drawings in schematic sectional representation. The multi-color electroluminescent panel shown in FIG. 11 is of a type comprising a plurality of electrodes 67, a plurality of common electrodes 62 formed on a substrate 61, two insulating layers 64 and 66 disposed between the electrodes 67 and the common electrodes 62 and a periodic structure of light emitting layers 65a, 65b and 65c disposed cyclically between the insulating layers 64 and 66 capable of emitting respective light of different colors.
The prior art multi-color electroluminescent panel shown in FIG. 12 is of a type comprising a plurality of electrodes 77, a plurality of common electrodes 72 formed on a substrate 71, two insulating layers 74 and 76 disposed between the electrodes 77 and the common electrodes 72, a single light emitting layer 75 disposed between the insulating layers 74 and 76 and a periodic structure of different color filters 78a, 78b and 78c arranged cyclically on the substrate 71 on one surface thereof opposite to the common electrodes 72.
In both of the prior art multi-color electroluminescent panels, any one of the light emitting layers 65a, 65b and 65c and the light emitting layer 75 is of a type having the light emission luminance versus applied voltage characteristic (characteristic of the light emission luminance relative to the applied voltage) which does not exhibit a hysteresis.
Specifically, the multi-color electroluminescent panel of the construction shown in FIG. 11 has a problem in that, since the color of light emitted from each of the light emitting layers is peculiar to material used to form the respective light emitting layer, the color cannot be selected as desired. Also, since the element has no hysteresis as described above, the prior art multi-color electroluminescent panel cannot be used in such an application that, when the panel comprising of picture elements with hysteresis is driven by the line sequential scanning method, the frequency of sustaining voltage pulses which are continuously applied to all picture elements of the panel can be, for example, about ten times the frame frequency at which write-in (light-on) pulses and erasing (light-off) pulses are applied, thereby to increase the number of lighting to increase the light emission luminance by a factor of 10. This application was reported in Digest 1976 SIP (Society for Information Display) Int. Symp. p.52. Accordingly, the prior art multi-color electroluminescent panel of the construction shown in FIG. 11 cannot be used in an environment where a high light emission luminance is desired.
On the other hand, the prior art multi-color electroluminescent panel of the construction shown in FIG. 12 cannot also be used in the way as described in connection with the electroluminescent panel of FIG. 11 because it does not exhibit a hysteresis. In addition, because of a loss of filter, the amount of light emitted to tile outside tends to be low, failing to provide a luminance of practically acceptable level.